Drugs which may aggravate MG

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Drugs which may aggravate MG

Dr Stanley Freedman

The important word in the title of this article is "may". Just as myasthenics differ widely in the sites and severity of their weakness, so they differ in their susceptibility to the effects of drugs, as, indeed, do non-myasthenics. There are, therefore, no absolute prohibitions, apart possibly from some of the drugs used in anaesthesia, and no need to panic if you are taking, or have taken, one of the drugs listed below without any ill-effects. If your MG is well-controlled, these drugs are very unlikely to have any ill-effects, and it is important not to deny yourself their benefits. Decisions about whether or not to take a drug must be made in consultation with your doctor. It should also be emphasised that while these drugs may make the symptoms of MG worse, none of them affects the basic disease process, apart from penicillamine.

From the doctor's viewpoint, problems arise because information on the drugs, in reference books as well as in the packaging, is often inaccurate. Some drugs, temazepam being a good example, are labelled as being absolutely contra-indicated in MG, when in fact they do not affect it at all, while on the other hand, some drugs which commonly aggravate MG do not carry a warning. Further problems arise for doctor and patient, because of the profusion of available drugs. For example, no fewer than 15 different "beta-blockers" are licensed for use in the UK, and any one of these may be marketed by several companies under different brand names.

In this article, I have listed drugs according to their class, and provided both "official" name, in bold, and trade names, where these are different, in italic. Popular mixtures which contain the offending drug are listed (in brackets). I have attempted a brief outline of how they may affect MG. As well as tablets and injections, I have listed preparations used locally in the eye, as significant amounts of drug can be absorbed into the bloodstream when given by this route.

Also, beware of laxatives, which can impair the absorption, and therefore the effectiveness, of all your drugs, but particularly of pyridostigmine (mestinon).

1. ANTI-ARRHYTHMICS

These are used to treat and prevent irregular heart beat. The ones in this list have largely been superseded by newer, safer, drugs, including beta-blockers (see below).

• Procaine Amide Pronestyl

· Quinidine Kinidin Durules

2. ANTIBIOTICS

These are used to prevent and treat bacterial infections. One group (A), which contains six members, affects transmission between nerve and muscle, and therefore can make MG worse. They are chiefly given by injection, and you are therefore most likely to come across them in hospital. You are more likely to encounter those in groups B, which are usually given as tablets, often for chest infections, but which are much less likely to upset your MG, and C, which are commonly used for bladder and kidney infections. Group D is now used very rarely.

• A.

  • Gentamicin Genticin, Genticin Ear/Eye drops, Cidomycin Injection, Cidomycin Ear/Eye drops/ointment

  • Amikacin Amikin

  • Netilmicin Netillin

  • Tobramycin Nebcin

  • Streptomycin

  • Kanamycin Kannasyn

• B.

  • Tetracycline Achromycin, Sustamycin, Tetrabid, Tetrachel, Deteclo, (Mysteclin).

  • Doxycycline Nordox, Vibramycin,

  • Limecycline Tetralysal 300

  • Minocycline Minocin MR

  • Oxytetracycline Terramycin

• C.

  • Ciprofloxacin Ciproxin

  • Acrosoxacin Eradicin

  • Cinoxacin Cinobac

  • Nalidixic Acid Mictral, Negram, Uriben

  • Norfloxacin Utinor

  • Ofloxacin Tarivid

• D.

  • Polymixin B

  • Colistin Colomycin Injection

3. ANTI-MALARIALS

These drugs are sometimes also used to treat rheumatic conditions.

• Chloroquine Avloclor, Nivaquine

• Hydroxychloroquine Plaquenil

4. ANTI-RHEUMATIC DRUGS

• Penicillamine Distamine, Pendramine.

5. ANTI-SPASMODICS

These drugs, which are used to relax and reduce the activity of the bladder and bowels, act by opposing the action of acetyl-choline (whereas drugs like mestinon promote it), and therefore carry a warning against their use in patients with MG. In fact, theoretically, they should not interfere with the action of acetyl-choline on muscle, and in practice there have been no reports of adverse effects in MG - perhaps because the warning has been so effective!

• Flavoxate Urispas

• Oxybutinin Cystrin, Ditropan

• Propantheline Probanthine

6. BETA-BLOCKERS

These drugs are used for the treatment of angina and other forms of heart disease, high blood pressure, migraine, and, occasionally, anxiety. They commonly produce a feeling of fatigue or muscle weakness, which tends to improve with continued treatment, and, rarely, have been reported to induce MG.

• Propranolol Inderal, Angilol, Apsolol, Bedranol, Berkolol, Beta-Prograne, Cardinol, Propanix, (Inderetic, Inderex)

• Atenolol Tenormin (Tenif, Tenoretic, Tenoret 50, Co-Tenidone), Atenix, Antipressan, Kalton, Totamol, (Beta-Adalat, Co-Tenidone, Totaretic)

• Acebutolol Sectral (Secadrex)

• Betaxolol Kerlone

• Bisoprolol Emcor, Monocor, (Monozide)

• Carvedilol Eucardic

• Celiprolol Celectol

• Esmolol Brevibloc

• Labetalol Trandate

• Metoprolol Betaloc, Lopresor, (Co-Betaloc)

• Nadolol Corgard

• Oxprenolol Trasicor, (Trasidrex)

• Pindolol Visken, (Viskaldix)

• Sotalol Beta-Cardone, Sotacor, (Sotazide, Tolerzide)

• Timolol Betim, Blocadren, (Moducren, Prestim, Timoptol Eye-drops).

7. DRUGS USED IN EPILEPSY

• Phenytoin Epanutin

This is always listed among drugs which can precipitate MG, but actual reports of problems are rare.

8. DRUGS USED IN PSYCHIATRY

A. Chlorpromazine and related drugs. These drugs are used in a wide variety of conditions. The original members of the group, chlorpromazepine and promazine, were reported to aggravate, or even to precipitate MG, but there are now a lot of newer analogues, and reports of trouble from these are rare. However it is probably still wise to use them cautiously.

• Chlorpromazine Largactil

• Clozapine Clozaril

• Flupenthixol Depixol

• Fluphenazine Moditen

• Loxapine Loxapac

• Methotrimeprazine Nozinan

• Oxypertine

• Pericyazine Neulactil

• Perphenazine Fentazin

• Pimozide Orap

• Prochlorperazine

• Promazine Sparine

• Risperidone Risperdal

• Sulpiride Dolmatil, Sulpitil

• Thioridazine Melleril

• Trifluoroperazine Stelazine

• Zuclopenthixol Clopixol Acuphase

• B. Lithium Camcolit, Liskonum, Li-liquid, Litarex, Priadel.

• C.

  • Phenelzine Nardil,

  • Isocarboxazid Marplan

  • Tranylcypromine Parnate, (Parstelin)

9. MUSCLE RELAXANTS

These drugs are designed to cause muscle paralysis and are used almost exclusively by anaesthetists. For this reason, I consider it unnecessary to list them individually. There are two classes of muscle-relaxants: curare-like drugs, which must not be used in MG, and depolarising relaxants, which can sometimes be used. Both types must be distinguished from drugs such as the minor tranquillisers, which are often called "muscle-relaxants", although their effects are entirely non-specific.

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